1. Field of the Invention
The present invention relates to semiconductor lasers. More particularly, it relates to buried active-layer-type double-heterojunction semiconductor lasers and to a method for producing them.
2. Description of the Prior Art
Semiconductor lasers having various structures have been, heretofore, proposed. For the purpose of decreasing the threshold current of a semiconductor laser and stabilizing the transverse mode of the laser beam, for example, a so-called buried heterostructure laser and a so-called channeled substrate buried heterostructure laser have been proposed.
In the case of the above-mentioned conventional lasers, it is preferable to make a width of a stripe active layer approximately one micrometer to stabilize the transverse mode. In order to increase the available output power of a laser, it is necessary to enlarge an emitting area (i.e., the sectional area) of the active layer. However, when the emitting area is enlarged by increasing the width of the stripe active layer, the transverse mode becomes unstable. Furthermore, since it is difficult to mass produce a conventional laser having a stripe active layer width of 1 .mu.m, a conventional laser having a stripe active layer width of 2 to 3 .mu.m is produced. In this case, when the laser output power becomes 2-3 mW, the laser oscillates a higher order modes.